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tals are concentrated in vertical-tube evaporators with exhaust steam at . and a vacuum of 26 in., at the rate of 1M gal. per square foot. Sodium >onate is separated in salt filters and a rapid circulation between salt filter
evaporator must be maintained in order to prevent crystallization of the >onate on the tubes.   Evaporators are built of cast iron with steel or char--iron tubes. Sodium Chloride (Common salt).—One ton of salt will require the evapora-
of about 3 tons of water from a saturated brine. All fine-grained salt iuum salt) is made in single- or multiple-effect, evaporators of the Standard 5 with deep cone bottoms, which will give a capacity of from 1J4 to 1M gal. square foot, with a steam pressure of 5 Ib. and a vacuum of 28 in. Usually e evaporators have large central downtakes, and in some cases, special >ellers for better circulation of the brine. Very large units have been built VEanistee, having a capacity of from 300 to 500 tons of salt per day. Salt covered in closed filters, by continuous vacuum filters, or with bucket eleva-Evaporation is retarded by incrustations of salt, and very frequently by ng of the tubes. Without proper treatment of the brine, this scale has to be )ved mechanically once a day. Some of the brines will foam considerably, a high-vapor space is necessary. Evaporators are usually built with cast-shells and copper or brass tubes. Sometimes iron tubes are also used, hoarse-grained salt, so-called "grainer salt,77 is manufactured in large shallow i made of steel or concrete, and heated by coils. The salt is removed con-Dusly by scrapers which drag along the bottom of the pan. With low-pres-steam these grainers have a capacity of from % to H gal. of water evaporated square foot of heating surface.
iodium Chlorate.—Liquors are concentrated from about 40 to 56 per cent, sodium chloride is separated. The work is usually done in horizontal-tube pecial vertical-tube double-effect evaporators in counter-current, with a n pressure of 5 Ib. and a vacuum of 26 in., at a rate of 0.8 gal. per square foot, ^orator shells and tubes should be of cast iron. odium Hydroxide (Caustic soda).—Liquors are usually concentrated
10 to 46 per cent in vertical-tube multiple-effect evaporators with a steam sure of 20 Ib. and a vacuum of 27 to 28 in., at the rate of-from 1 to 1J4 gal. quare foot. Sodium carbonate and chloride are separated during the evapo-g process, and are recovered in salt filters. Evaporators are usually built of iron or steel, with steel or charcoal-iron tubes. For the more concentrated TS copper tubes have also been used successfully.
he 46 per cent solution is further concentrated to 80 per cent in the Mantius concentrator with a steam pressure of 100 Ib. and a vacuum of 27 in. at the rate of il. per square foot. Evaporator of cast iron, tubes of special cast iron or copper. odium Nitrate.—Solutions are concentrated from 30 to 70 per cent in a cal-tube evaporator with a steam pressure of 5 Ib. and a vacuum of 27 in., e rate of 0.9 gal. per square foot. For larger quantities a double or triple •j operating counter-current is used. Evaporators are built of cast iron, tubes arcoal iron or copper. Sodium chloride is separated during the first stage aporation and sodium nitrate during the final concentration. odium Nitrite.—Liquors are concentrated from 30 to 80 per cent in a ontal-tube machine with a steam pressure of 5 Ib. and a vacuum of 26 in.,